Limb rotation is valuable—if not essential—for performing daily tasks. For example, forearm and humeral rotations are important motions employed in virtually all activities of daily living and are essential motions for controlling upper limb prostheses. Femoral rotation is not typically provided for lower limb prostheses, but if available, would allow lower limb amputees to more easily perform activities such as dressing or transferring in and out of vehicles. Currently, passive devices constitute the majority of commercially available prosthetic rotators. Passive control is achieved by manually positioning the devices or by manipulating the devices against a stable object.
Body-powered and myoelectric wrist rotators are also available, but are fitted much less frequently. Body-powered control uses biscapular abduction to control the rotator through tensioning a cable system, and allows the user to lock the wrist or humeral rotator in various positions. Myoelectric control is based on measurements of electromyogram (EMG) signals of agonist-antagonist muscle pairs to control a motorized prosthetic rotator. Both active control methods operate all components sequentially and utilize muscles that do not necessarily relate to arm rotation. As a result, the rotational control of the arm is slow, unnatural, and cannot maintain inherent proprioceptive awareness of limb rotation. Since the amputees cannot feel the orientation of their prosthesis, they must use visual feedback to determine how their artificial limb is positioned in space. This lack of proprioceptive feedback impedes prosthetic control, increases the cognitive burden of using a prosthesis and impairs functions in all applications.
The only available mechanisms of femoral rotation available to lower limb amputees are passive femoral rotators, and they are rarely prescribed. Existing upper limb prosthetic rotators have not been adapted for rotation of lower limb prostheses because lower limb prostheses are all passively controlled; there is currently no analog in the lower limb to body-powered or myoelectric control in the upper limb. Therefore, even if such a device were available, the amputee would have no way to control it.
One known method to improve voluntary control of prosthesis rotation is to physically couple the rotation of the bones remaining in the residual limb to the prosthetic rotation. For example, two interfacing mechanisms have been developed to create a physical connection between the residual humerus and the prosthesis for control of the prosthesis rotation, osseointegration and artificial epicondyles. Osseointegration is a direct structural connection between residual bone and the prosthesis. This technique involves implanting a titanium bolt into the bone of the residual limb. An abutment attaches to the bolt and protrudes through the skin to provide direct attachment to the prosthesis so that the manipulation of the prosthesis including prosthesis rotation follows movement of the bone. Another attachment method is the use of artificial epicondyles that are created by surgically inserting an implant into the residual bone and covering the implant with soft tissue and skin. The artificial epicondyles can suspend the prosthesis and provide the function of rotation of the prosthesis.
Patients using such systems employing osseointegration and artificial epicondyles have rotation control with preservation of proprioception for rotation of their artificial limb in the longitudinal axis of the residual limb. However, these approaches have significant drawbacks. For example, direct skeletal attachment may give rise to infections at the skin interface and the implants may loosen over time. Also, loading of the skin over artificial epicondyles can cause skin breakdown and there is similarly a potential for loosening of the implants. Both systems require extensive surgical procedures and significantly delay use of the prosthesis as the implants integrate with the residual bone matrix.
The present invention provides improved rotational control of prostheses while avoiding the significant drawbacks of systems employing osseointegration and artificial epicondyles. Also, since the present invention instantaneously converts residual bone rotation into prosthetic limb rotation, it maintains inherent proprioceptive awareness of limb rotation reducing the cognitive burden of the use of the prosthesis while insuring accurate and natural rotation. Finally, the improved rotational control of the present invention will not compromise other applicable control sources, such as biceps and triceps EMG that can be used to operate other degrees of freedom such as wrist and hand movements. Therefore, the present invention can be readily combined with other prosthesis controls to achieve additional prosthesis functionality.